Technical Abstract:
Forage sorghum is one of the suggested crops to provide feedstock for biofuel production under water-limited conditions due to its stress tolerance and efficient water use; however, research is needed under these conditions to better understand its energy yield potential. This study presents results from a two year evaluation of biomass and potential cellulosic ethanol (EtOH) production potential of forage sorghum cultivars differing in brown midrib trait (bmr) under dryland (no irrigation) and limited irrigation (2.88 mm day-1; subsurface drip) in the semiarid Southern High Plains of the U.S. Commercial cultivar Sorghum Partners 1990 (SP1990, conventional non-bmr) produced significantly more biomass (29-62%) than a bmr12 cultivar PaceSetter bmr (PS bmr) under irrigated and dryland conditions during both years of this study. However, PS bmr biomass had higher cellulosic EtOH conversion efficiency than SP 1990 in both years according to simultaneous saccharification and fermentation analysis. Irrigation resulted in 26-49% more biomass and 28-72% more cellulosic EtOH production during both growing seasons, indicating that limited irrigation had favorable effects on both biomass and biofuel production. In the first year, when precipitation was below average, both cultivars produced similar amounts of cellulosic EtOH. During the second year, when precipitation was above average, higher biomass production of SP 1990 resulted in 28% higher cellulosic EtOH production than PS bmr when averaged across both irrigated and dryland. The large range of cellulosic EtOH production (1,600 to 3,380 L ha-1) during the two years of this study was primarily driven by differences in water availability that resulted from precipitation and irrigation. This study indicates that chemical composition and biomass yield potential of sorghum cultivars are critical factors that affect biomass and biofuel production under limited water conditions.